To make basic chords from the major and minor scales, start
with the first note, then skip to the third, then the fifth.
Using C Dorian, that’s C, Eb, G. This is called a triad,
and it’s the simplest type of chord.
To extend the chords, add in the seventh, the second/ninth,
the fourth/eleventh, and the sixth/thirteenth. Using C Dorian,
that’s Bb, D, F, A. The more notes you add, the more
complex and dense the chord becomes.
You can also skip or leave out notes: C, Eb, Bb, F for example.
Also, you can double notes (especially the first/root.)
It doesn’t matter what order the notes are in. C Eb
Bb is functionally the same chord as C Bb Eb (though they
will have slightly different feeling.)
Don’t put fourths/elevenths into major chords unless
you leave the third out, it sounds very dissonant.
Not surprisingly, chords have the same feel as the scale
they came from, so a chord made from Phrygian sounds very
Spanish.
Any combination of notes can be a chord, though if they don’t
come from a particular scale, they won’t make much sense.
But that can be good sometimes. For example, you can use clusters
(C, Db) and tritones (C, F#) to create tension and anxiety.
The blues scale is an oddball. You can’t make chords
from it, but it works equally well over major and minor chords.